The present invention relates to a heat-sensitive transfer recording medium useful for forming printed images on an image receptor comprising a polyester film or the like, by a thermal transfer method, and to a method for forming printed images using the same.
Heretofore, with a label printer or like printer utilizing thermal transfer technology, a heat-sensitive transfer recording medium is used to form printed images on a plastic film such as polyester film. The label printer is called various names such as tape printer. Herein, however, the name "label printer" is used.
Printed images formed on labels and the like are required to have excellent fastness such as scratch resistance and chemical resistance including alcohol resistance.
For this reason, heat-sensitive transfer recording media have used a colored ink layer containing one or more resins excellent in scratch resistance or alcohol resistance as a binder thereof.
With the conventional heat-sensitive transfer media having such a colored ink layer of single layer, however, it is difficult to obtain printed images excellent in both scratch resistance and alcohol resistance even though a resin having good scratch resistance and a resin having good alcohol resistance are used in combination. This is because the resin having good scratch resistance is not necessarily good in alcohol resistance and the resin having good alcohol resistance is not necessarily good in scratch resistance.
In order to solve this problem, a type of heat-sensitive transfer recording medium comprising a support, a transparent barrier layer provided on the support and composed of a polyester resin, an epoxy resin or the like, and a colored ink layer provided on the barrier layer and composed of a polyester resin or the like as a binder thereof (hereinafter referred to as "prior art A", see Japanese Unexamined Patent Publication Nos. 2-150391 and 2-160589) has been proposed. Another type of heat-sensitive transfer recording medium comprising a support, a colored ink layer provided on the support, and an adhesive layer provided on the colored ink layer and composed of a polyester resin or the like (hereinafter referred to as "prior art B", see Japanese Unexamined Patent Publication No. 4-27589) has also been proposed.
However, prior art A involves a problem of causing a tailing of the printed image due to poor separability of the barrier layer when being thermally transferred. Herein, the term "separability" of a transfer layer means the property that when being transferred, the heated portion of a transfer layer is easily separated from the unheated portion of the transfer layer and only the heated portion is transferred onto an image receptor to give a printed image with good definition. The term "tailing of the printed image" means the phenomenon that ink in an unheated portion in the neighborhood of the heated portion is transferred on the downstream side of predetermined ink dots to thicken lines constituting an image. Further, when the binder of the colored ink layer is different from that of the barrier layer, there also arises a problem that the colored ink layer is separated at the interface between the colored ink layer and the barrier layer and transferred. As a result the barrier layer is not present on the colored ink layer in the resulting the expected scratch resistance is not achieved.
Prior art B also involves the problem of causing a tailing of the printed image due to poor separability of the adhesive layer. Prior art B involves another problem that the colored ink layer, having small thickness in the resulting image, is exposed, resulting in poor scratch resistance.
In view of the foregoing, it is an object of the present invention to provide a heat-sensitive transfer recording medium capable of forming printed images of both excellent scratch resistance and excellent alcohol resistance by allowing respective resin binders used in the ink layer to fully exhibit their own functions.
This and other objects of the present invention will become apparent from the description hereinafter.